Make altitude in Location optional

When specifying a device location in the TTN console and leaving the
altitude at 0, it will not be part of the payload. Right now this causes
the parser to fail.

Regression test included.

Author: dbrgn

src/v3/mod.rs

@@ -99,7 +99,9 @@ pub struct DataRateLora {
 pub struct Location {
     pub latitude: f64,
     pub longitude: f64,
-    pub altitude: f64,
+    #[serde(default)]
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub altitude: Option<f64>,
     pub source: String,
 }
 
@@ -194,4 +196,15 @@ mod test {
 
         assert!(matches!(uplink.payload, Payload::Uplink(_)));
     }
+
+    /// Regression test: Altitude in location may not be present.
+    #[test]
+    pub fn uplink_without_altitude() {
+        let json = include_bytes!("../../test/v3/uplink3.json");
+        let uplink: Message = serde_json::from_slice(json).unwrap();
+
+        println!("{:#?}", uplink);
+
+        assert!(matches!(uplink.payload, Payload::Uplink(_)));
+    }
 }

test/v3/uplink3.json

@@ -0,0 +1,72 @@
+{
+  "end_device_ids": {
+    "device_id": "some-device-id",
+    "application_ids": { "application_id": "some-app" },
+    "dev_eui": "FFFFFFFFFFFFFFFF",
+    "join_eui": "0000000000000000",
+    "dev_addr": "77777777"
+  },
+  "correlation_ids": ["gs:uplink:01JZG5HJ5E6Q6RS9QB9T9BZZXM"],
+  "received_at": "2025-07-06T15:26:44.606958589Z",
+  "uplink_message": {
+    "session_key_id": "q2P5jLF9Qldmi11CkZU7bg==",
+    "f_port": 3,
+    "frm_payload": "aGVsbG8=",
+    "rx_metadata": [
+      {
+        "gateway_ids": {
+          "gateway_id": "some-gateway",
+          "eui": "AAAAAAAAAAAAAAAA"
+        },
+        "time": "2025-07-06T15:26:44.342732906Z",
+        "timestamp": 12854260,
+        "rssi": -33,
+        "channel_rssi": -33,
+        "snr": 12,
+        "location": {
+          "latitude": 47.0000000000000,
+          "longitude": 8.00000000000000,
+          "altitude": 500,
+          "source": "SOURCE_REGISTRY"
+        },
+        "uplink_token": "cmVkYWN0ZWQtdXBsaW5rLXRva2Vu",
+        "received_at": "2025-07-06T15:26:44.344797626Z"
+      }
+    ],
+    "settings": {
+      "data_rate": {
+        "lora": {
+          "bandwidth": 125000,
+          "spreading_factor": 12,
+          "coding_rate": "4/5"
+        }
+      },
+      "frequency": "868300000",
+      "timestamp": 12854260,
+      "time": "2025-07-06T15:26:44.342732906Z"
+    },
+    "received_at": "2025-07-06T15:26:44.399177939Z",
+    "consumed_airtime": "1.482752s",
+    "locations": {
+      "user": {
+        "latitude": 47.55555555555555,
+        "longitude": 8.555555555555555,
+        "source": "SOURCE_REGISTRY"
+      }
+    },
+    "version_ids": {
+      "brand_id": "dragino",
+      "model_id": "lsn50v2-d20",
+      "hardware_version": "_unknown_hw_version_",
+      "firmware_version": "1.1",
+      "band_id": "EU_863_870"
+    },
+    "network_ids": {
+      "net_id": "000013",
+      "ns_id": "BBBBBBBBBBBBBBBB",
+      "tenant_id": "ttn",
+      "cluster_id": "eu1",
+      "cluster_address": "eu1.cloud.thethings.network"
+    }
+  }
+}